The word biomass generally refers to substances of biological origin (e.g., agricultural products or by-products; lumber; plants; etc.) that can be utilized as an energy source or industrial raw material. Since biomass is produced by solar energy, and by the action of air, water, soil, or similar natural substances, it can be produced infinitely.
Fuel, methanol, and similar materials can be produced making use of the above-described biomass. Also, since biomass that exists in the form of waste can be utilized, a clean environment can be provided. Further, since newly produced biomass is grown through photosynthesis; i.e., fixation of CO2, the concentration of CO2 in the atmosphere is not increased.
Conventionally proposed methods for converting biomass into alcohol include, for example, the fermentation method and the hydrothermal degradation method. The former method, the fermentation method, requires installation of a tank for sugar components, whereas the hydrothermal degradation method involves the problems that high temperature and high pressure are required and yet yield is low. Moreover, another problem is that, considerable amounts of residue are generated from the input biomass, raising the problem of low biomass utilization.
Meanwhile, in the case in which biomass is gasified, a gasification furnace, such as a fixed-bed gasification furnace or a fluidized-bed gasification furnace, has heretofore been employed. However, since only the surface portions of granular biomass undergo reaction, and the reaction cannot proceed uniformly to the innermost portion of the granules, tar is generated, and the produced gas; i.e., the gas obtained through gasification, has a low H2 content and low CO content. Therefore, the thus-produced gas cannot serve as a raw material for methanol synthesis. Moreover, the generated tar is deposited not only onto the inside wall of the furnace, but also onto the apparatuses, etc. installed on the downstream side of the furnace, inviting problematic maloperation of the furnace.
In order to prevent such problems, conventionally, oxygen is supplied in great amounts so as to effect combustion at high temperature. However, in this case, another problem is involved; a high-temperature zone of higher than 1,200° C. is formed at some portions, where gasification of biomass does not proceed successfully, providing large amounts of soot through combustion of biomass.
In view of the foregoing, an object of the present invention is to provide a biomass gasification furnace which promises clean, high-efficiency gasification, which contemplates complete gasification of biomass, and which is capable of producing a gas realizing a highly efficient methanol synthesis. Another object of the present invention is to provide a methanol synthesis system making use of the thus-produced gas.